The present invention relates to a method of diagnosing the aging and fault of a glow plug, particularly, to a method of improving the reliability of diagnostic results.
Since the quality of a glow plug in an internal combustion engine such as a diesel engine considerably affects the startability of the diesel engine or the like, in the related art, various methods and apparatuses for diagnosing the quality, the state of aging of the glow plug have been proposed and put into practice.
For example, JP-A-11-182400 discloses an apparatus that is configured to detect the upstream and downstream voltages of the glow plug, and to be able to determine the open circuit of the glow plug based on a difference in the voltage.
JP-A-2002-276524 discloses an apparatus that is configured to be able to determine the open circuit of the glow plug by comparing the electric potential of a series circuit including the glow plug with a reference electric potential corresponding to the voltage of a power supply.
JP-A-2011-185128 discloses an apparatus that is configured to detect the resistance value of the glow plug multiple times, and to correct a voltage applied to the glow plug based on the detected resistance values.
Meanwhile, in the related art, the apparatuses disclosed in JP-A-11-182400 and JP-A-2002-276524 can detect the open circuit of the glow plug; however, since the apparatuses perform a detection process during operation of the internal combustion engine, cooling associated with air intake/exhaust or fuel injection may cause a change in the resistance value of the glow plug, and thereby, the apparatus cannot accurately detect resistance values and the state of aging of the glow plug, which is a problem.
In the related art, the apparatus disclosed in JP-A-2002-276524 has a problem in that the only correction to the applied voltage contrarily promotes the aging of the glow plug.